Hydraulic booster valve

Abstract

The present invention is a gain valve for a hydraulic booster which allows transition from a manual braking mode to a power assist braking mode without the control called for in the manual mode immediately applied when the power assist function begins to operate. This is accomplished by a bypass passage through the gain valve piston which prevents a pressure increase in the hydraulic booster for power assisted braking. The bypass passage automatically opens and resets in response to system pressures.

What is claimed is: 
     
       1. A gain valve for a hydraulic booster, comprising: a gain valve housing having a front end and a back end;   a first chamber disposed in the housing in spaced relation from the front end of the housing, there being a front inlet passage through the housing into the first chamber;   a second chamber coaxially connected to, and communicating with, the first chamber and extending therefrom towards the back end of the housing, the second chamber having a greater cross-sectional area then the first chamber, there being an outlet passage through the housing from the second chamber;   a gain valve bore coaxially connected to, and communicating with, the second chamber and extending therefrom towards the back end of the housing, there being a side inlet passage from the bore through the housing in spaced relation from the back end thereof;   a gain valve piston having a front end spaced from a back end and slidably located in the bore, the piston having a cross-sectional geometry enabling it to be slidably received in the second chamber and the first chamber and forming in at least the second chamber an annular opening through which fluid flows between the inlet and outlet passages of the first and second chambers, the piston being sized to close the annular opening as it enters the first chamber to block the flow of fluid through the opening, the piston having a back end chamber which extends longitudinally of the piston from the back end thereof and which has a back end inlet passage extending radially therefrom, the back end inlet passage being positioned to communicate with the side inlet passage in the bore, until the piston enters the first chamber;   a spring disposed in the back end chamber of the piston and coacting between the piston and back end of the housing to bias the piston towards the front end of the housing;   means, responsive to an increase of fluid pressure in the first chamber as the piston moves closer thereto, to stop movement of the piston towards the first chamber and prevent the piston from entering therein; and   means for maintaining the first chamber and front inlet passage thereof in fluid communication with the second chamber and outlet passage thereof when the fluid pressure in the first and second chambers decreases to a point where the biasing force of the spring moves the piston into the first chamber, said maintaining means including an opening in the front end of the piston in communication with the first chamber, the opening extending longitudinally into the piston from the front end thereof, and at least one radially oriented passage disposed in the piston and connecting the opening therein with the second chamber and outlet passage thereof, the radial passage of the piston being located so that it is sealed within the gain valve bore when the piston is outside the first chamber.   
     
     
       2. The gain valve as recited in claim 1 further comprising a means to seal between the gain valve piston and the gain valve bore wall between the front end and the back end of the gain valve piston. 
     
     
       3. The gain valve as recited in claim 2 wherein the gain valve bore is cylindrical having a diameter slightly greater than the diameter of the gain valve piston, the first chamber being cylindrical and having a diameter equal to the gain valve bore, and the second chamber having a greater geometric cross section than the first chamber. 
     
     
       4. The gain valve as recited in claim 1 wherein the means to stop movement of the piston includes: a first chamber wall in the front of the first chamber;   a gain valve stem extending axially from the gain valve piston through a stem hole in the first chamber wall;   a pressure limiting piston, having a front portion and a back portion, the front portion passing slidingly through a pressure limiting bore through the back end of the gain valve housing, and the back portion of the pressure limiter is located in a pressure limiting chamber on the opposite side of the first chamber wall, the pressure limiting piston having a common axis with the gain valve stem, there being a pressure chamber passage through the gain valve housing to the pressure limiting chamber;   a means to bias the pressure limiting piston toward the front end of the gain valve housing;   a stopping means between the front portion and the back portion of the pressure limiting piston to prevent the pressure limiting piston from sliding through the pressure limiting bore and located so that during manual operation the gain valve piston sidewall opening is in communication with the second chamber.   
     
     
       5. The gain valve as recited in claim 4 wherein the stopping means is an extension from the piston wall which is in the pressure limiting chamber and intersects the wall surrounding pressure limiting bore when the pressure limiting piston slides toward the front end of the gain valve housing. 
     
     
       6. The gain valve as recited in claim 5 wherein the means to bias the pressure limiting piston includes a spray between the extension and the first chamber wall. 
     
     
       7. A gain valve of a booster for a fluid operated mechanism such as a power brake, comprising: a housing having at least three coaxially aligned communicating chambers, the second chamber between the first and third chambers having a greater diameter than the first and third chambers; a fluid inlet passageway in the first chamber and a fluid outlet passageway in the second chamber; a gain valve piston reciprocable in the third chamber and extending therefrom into the second chamber and forming with the second chamber an annular opening through which fluid passes between the passageways, the piston being capable of closing the opening as it enters the first chamber; means for biasing the piston in the direction of the first chamber; means coacting with the piston and responsive to an increase in fluid pressure in the first chamber as the piston approaches closer thereto, for limiting movement of the piston in the direction of the first chamber to prevent closure of the opening; and characterized by means for maintaining the passageways in fluid communication should the piston enter the first chamber and close the opening so that fluid is free to flow between the passageways. 
     
     
       8. The booster of claim 7, wherein the means for maintaining the passageways in fluid communication includes, a passage extending longitudinally within the piston in communication with the first chamber and fluid inlet passageway when the piston enters the first chamber, and at least one radially oriented passage in the piston between the longitudinal passage and second chamber, the radially oriented passage being located such that it will be sealed in the third chamber when the opening is open and not closed. 
     
     
       9. The booster of claim 8, wherein the means for limiting movement of the piston includes a fourth chamber in coaxial alignment with the first chamber and sealed therefrom, the fourth chamber being in farther spaced relation from the second chamber than the first chamber, a piston reciprocable in the fourth chamber and movable towards the first chamber in response to an increase of fluid pressure in the first chamber as the piston approaches closely thereto, means for biasing the piston in the fourth chamber in a direction away from the first chamber, and a stem extending from the gain valve piston in coaxial alignment therewith into the fourth chamber for contacting the piston in the fourth chamber upon predetermined relative movement of the pistons towards each other.